I believe the only known LSD overdose that resulted in death was someone who INjECTED it in the Gram range. A gram of LSD is around 10,000 hits. I believe its pretty hard to kill yourself with acid.
As far as I know, people that develop mental disorders after an intense trip, do so because it already existed and just hadn't surfaced yet. This can happen on one hit or one hundred.
I've had several high dose trips(10 strip range) and lived to tell the tale.
I have friends who buy a sheet about once every two or three months and consume three or four hits at a time until its all gone, staying up for four or five days. They are a "little" strange, but not crazy, and able to hold down jobs, continue their education, etc.
Every bad trip I've ever had resulted from one of two things, either I was depressed before consuming it or something really shitty happened during the course of the trip that changed its tone. Its never been spontaneous. Acid is not a drug you take to cheer you up when your down.
If you want to take 20 hits of acid, you will probably be alright. Being out in public, however, is a stupid idea. When you're that out of touch with reality people DO notice, and most people know what someone on drugs looks like.
Besides the possibility of people recognizing that your on drugs and having you arrested, your in danger of hurting yourself and others.
If you desire to consume high doses of acid, my suggestion is to do it at someone's home, or out in nature. Have a group of people with you who are also going to be tripping, and have at least one person there to babysit.
Be Safe, Be Responsible. Check out erowid for high dose acid reports and read about the experiences of others.
Love,
Pure
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Intelligence is not best measured by the answers you have but by the questions that you ask